Production of cellulosic structures



Patented May 2, 1944 2,347,883 PRODUCTION OF CELLULOSIC STRUCTURES Norman Louis Cox, Claymont, Del., assignor to E. I. du Pont de N emours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application November 3, 1942, Serial No. 464,387

6 Claims.

This invention relates to the manufacture of regenerated cellulose structures from viscose. More particularly, the invention relates to improvements in the process of forming regenerated cellulose structures from viscose in a coagulating bath and stretching the formed structures to improve the tenacity thereof. Although the invention is generally applicable to the preparation of filaments, yarns, films, caps, bands, ribbons, and other similar structures of regenerated cellulose, it will, for convenience, be discussed with particular reference to the production of viscose rayon yarn,

It has long been known that the dry tenacity of a viscose rayon yarn can be increasedby increasing the spinning tension employed in the spinning of the yarn. Such increase in tenacity is, however, generally accompanied by a decrease in elongation and loop strength of the yarn.

The presence of from 0.1% to 1.0% zinc sulfate permits the spinnin of viscose rayon yarn at higher spinning tension without decreasing, to the same extent, the elongation and loop tenacity of the yarn. Generally, however, 1% represents the highest concentration of zinc sulfate which can be practicably used. Higher concentrations of zinc sulfate cause severe craterlng of spinneret openings with a resultant adverse effect on the spinning operation.

It is therefore, an object of this invention to provide a process whereby regenerated cellulose structures, such as yarn, of improved physical properties can be spun without; at the same time, introducing spinning difliculties such as spinneret cratering that will make the process impractical for general use on a large scale.

It is another object of this invention to provide an improved process for the high tension spinning of regenerated cellulose structures from viscose.

It is a further object of this invention to provide a process for the production of a viscose rayon yarn possessing improved physical properties including a high tenacity, a desirableelongation, and a greatly improved loop strength. 1

Other objects of the invention will appear hereinafter.

These objects may be accomplished, in general, by the extrusion of a viscose solution into a sulfuric acid spinning bath containing from 1% to 8% manganous sulfate and from 0.1% to 1% of zinc sulfate. The spinning bath may, of course, also contain the usual amounts of sodium sulfate, glucose and/or ammonium sulfate.

It has now been found that the addition of 1% ning bath containing 0.1% to 1% zinc sulfate will permit a higher spinning tension of the viscose rayon yarn than by the use of the zinc sulfate alone. The addition of the manganous sulfate will not cause severe cratering of the spinneret openings. However, it is necessary that the bath contain the zinc sulfate as well as the manganous sulfate in order to obtain these improved spinning properties of the bath resulting from the use of the manganous sulfate.

It has furthermore been found that the addition of the manganous sulfate to the bath will permit the lowering of the sulfuric acid content of the bath thereby lowering the rateof regeneration of the viscose and permitting the spun filaments to remain longer in a plastic state. In the plastic state, the filaments are more responsive to stretching conditions. It is thus possible to spin a viscose rayon yarn with higher spinning tension to produce stronger yarn without objectionably lowering the elongation and loop strength of the yarn. The increased loop strength of the yarn is particularly important since it is a measure of the fatigue resistance of the yarn.

(Loop strength in grams per denier is the force in grams necessary to break one or both of two interlocked loops of yarn divided by twice the denier of the yarn. The loop strength is measured in grams on the same type of machine used for measuring dry tenacity, the break occurring .bodiments of the invention.

Cotton linters viscose containing 7 per cent cellulose and 6 per cent caustic (i. e., 7-6 viscose) is allowed to ripen to a salt index of 4.0 and is spun into filaments (150 denierfilaments) by extruding the same through a spinneret having holes of .0035 inch diameter into a coagulating and regenerating bath comprising per cent H2SO4, 20 per cent NazSO4, 4 per cent glucose, 0.7 per cent ZnSOi, and 5 per cent MnSO4. The bundle of filaments is given a bath travel of inches by using a 6-roller set-up. Sumcient vanes on the rollers and roller end guides were used to produce a spinning tension of 0.83 g./d. The apparatus and general procedure used to lead viscose into the bath and to collect the formed to 8% manganous sulfate to a sulfuric acid spin- 55 thread are essentially the same as those used commercially in the so-called bobbin or spool process. The specific conditions include a temperature of 52 C. and a windup speed of 3500 inches per minute. The resulting regenerated cellulose gel yarn is washed free of acid and salt and dried on the bobbin. The dried yarn is twisted 4 turns per inch, and tested after conditioning at 25 C.-50 per cent relative humidity for 48 hours. The yarn prepared inaccordance with this example has a loop strength of 2.54 g./d. as compared to 2.03 g./d. for a control yarn spun into a bath containing 11% sulfuric acid, 23% sodium sulfate, 4% glucose and 0.85% zinc sulfate under the same operating conditions. The wet and dry tenacities (1.85 and 3.05 g./d.) and the wet and dry elongations (19.4 and 11.4 per cent) are as good as for the above control yarn. This example clearly illustrates the improved loop strength imparted to yarn by the addition of manganous sulfate to a spinning bath containing zinc sulfate.

Example II Tenacity, Elongation,

g./d. percent Loop Bath composition strength,

g, Dry Wet Dry Wet 7.0-2o-4-0.85-5.0(H,SOl-Na=S0 glucose-ZnS04-MnS0i 3.14 1.85 9.9 16.6 2.50 11-23-4-035 (Hzsoa-Nllzsor glucosaZnSOi) 3.24 2.1 9.3 17.0 2.03

Example III A commercial viscos containing 7% cellulose (cotton linters) and 6% alkali is spun at a sodium chloride index of 5.0 into an aqueousregenerating bath containing 8% sulfuric acid, 20% sodium sulfate, 4% glucose, 0.85% zinc sulfate and manganous sulfate (MnSO4) at a temperature of 52 C. For comparison another yarn is spun under similar conditions but containing no zinc sulfate. In the latter case the regenerating bath employed container 8.2% sulfuric acid, 20% sodium sulfate, 4% glucose, and 5% manganous sulfate. In both cases, viscose is spun into filaments (150 denier 60 filaments) by extruding the same through a spinneret having .0035 inch hole size. The total travel in the coagulating and regenerating bath is approximateiy 160 inches; this travel is obtained by using a system of roller guides which are adapted to produce gradually increasing tension on the thread. The tension on the thread at the point of its emergence from the bath is 0.83 grams per denier. The thread is collected on a bobbin at 3500 inches per minute. Immediately after collection, it is washed fre of acid and salt and dried on the bobbin. The dried yarn is twisted 4 turns per inch, and tested after conditioning at 25 C.-50% relative humidity for 48 hours. The important advantage for the use of the combination of zinc sulfate and mang-anous sulfate in connection with gel swelling, maximum break tension, and loop strength of finished yarn is not realized for baths containing manganous sulfate without zinc sulfate, as will appear from the following table. In a bath containing manganous sulfate without zinc sulfate the gel swelling is mor than 10% higher than the minimum gel swelling obtainable and the maximum break tension is quite low as can be seen below in the table. The loop tenacity is correspondingly low.

'A modified coagulating and regenerating bath containing 10 per cent H2504, 20 per cent NazSOt, 4.. per cent glucose, 0.85 per cent ZnSO'4, and 5 per cent MnSO4 is used to spin denier yarn from regular 76 viscose under conditions described in Example I. Maximum spinning tensions are measurably higher than in similar baths in the absence of manganous sulfate which makes it possible to operate at tensions not permissible in straight H2SO4-NazSO4-glucose-ZnSOr baths. The resulting super-tenacity yarns spun in this manner have wet and dry tenacities and elongations comparing favorably with those obtained in the 11-234-0.85 (HzSO4-Na=SO4-glucose-ZnSO4) bath while the loop strength is decidedly better Viscose containing 7 per cent cellulose and 6 per cent caustic is spun into a bath containing 7.0 per cent H2804, 20 per cent NazSOr, 4 per cent glucose, 0.7 per cent ZnSO-r, and 3 per cent M11804. All conditionsused in producing and processing the threads are similar to those in Example I. The loop strength of the resulting yarn is 2.53 g./d. as compared to 2.03 for a control yarn spun into an ll-23-4-0.85 (H2804- NaiiSO4-glucose-ZnSO4) bath. (See Example I.)

Example VI A commercial viscose containing 7 per cent cellulose and 6 per cent caustic at a sodium chloride .indexof 5.1 is spun into an aqueous regenerating bath containing 7.5 per cent H2804, 20 per cent Naasoi, 4 per cent glucose, 0.7 per cent ZnSOr and 3 per cent MnSO-r at a temperature of 52 C. The 60 filament-150 denier yarn is given a total bath travel of inches over a set of 2,347-,sss

and retain this crimped form unchanged through the washing, purifying and drying process.

Example VII Filaments produced in the same manner as in Exampl VI are allowed to dry under tension on the bobbin. When they are relaxed in hot water in the form of loose skeins, continuous filament crimped yarn is obtained.

. The preferred method of operating the present invention is as follows: A

Manganous sulfate in amounts of 2% to 5% is dissolved in the coagulating and regenerating bath containing 7-11% sulfuric acid, 18-23% sodium" sulfate, -4% glucose and 0.5-1% zinc sulfate. Viscose is ripened to a salt index of 4-6 and then forced through a spinneret into the modified coagulating and regenerating bath at a temperature between 45 C. and 55 C. The filaments are stretched in the bath to a high tension (at least 0.3 gram per denier). For the production of high tenacity viscose rayon yarns for use in the preparation of tire cords With improved fatigue resistance, it is particularly desirable to use the lowest sulfuric acid concentration which is practical for obtaining good spinning performance. Th bundle of filaments is preferably given a bath travel of from 130-250 inches by means of a multiple roller spinning set-up, consisting of.from 6-10 roller guides. These roller guides function to gradually apply tension to the'traveling filaments, thereby orient ing the micelles therein while they are still somewhat plastic.

Viscose used in the preparation of filaments in accordance with the present invention is not restricted to any type; for example, it may be prepared from cotton linters, wood pulp or mixv tures of the two. The composition of the viscosemay be varied. For example, it may have a cellulose content of between 13-12% and it may have an alkali content of between 48%. The salt index of the viscose may vary between 3 and 7. 1

Although the above mentioned commensare preferred to obtain'th maximum benefit from the invention, definite advantages will be obtained by carrying out the invention within the following broader limits. l

The spinning bath may contain from -11% sulfuric acid, 18-25% sodium sulfate, 04% glurose, (Ll-1% zinc sulfate, and 1-8% manganous su fa-t0. ThHpresence of ammoniumsulfate, magnesium sulfate and other modification agents commonly used by those skilled in the art will not interfere with the beneficial action of manganous sulfate. The temperature of the spinning bath should be maintained between 40 C. and 65 C. I

The concentrations of the various substances used in the spinning bath should be adjusted to each other and to the composition of the viscose. For example, for viscose containing 7% cellulose and 6% caustic, when approximately 5% manganous sulfate is used in the spinning bath, the sodium sulfate content of the spinning bath should be maintained between approxim tely 18-23%. When glucose is omitted from the coagulating bath, the sodium sulfate content is preferably nearer the upper limit of solubility. The optimum sulfuric acid content of the spinning bath is,'0f course, dependent upon the other constituents in the bath as well as such important viscose variables as cellulose and caustic content. It is necessary to increase the bath acid bath of varied composition and temperature acidity as the concentration of sodium sulfate and glucose increases, while it should be decreased with the addition of manganous sulfate. As the sodium hydroxide content of the viscose is reduced from 6% to 4%, the optimum bath acidity is correspondingly lowered.

Th abov variables are preferably so adjusted as to produce a regenerated cellulose gel filament which has substantially the minimum gel swelling characteristics and highest break tension, properties which are usually associated with the best yarn properties and operating efficiency.

The gel swelling characteristic of a thread is measured in the following manner:

A single layer of thread is collected on a bobb n by manually operating the traverse mechanism with the threadspinning 3500 inches per minute with a 25 inch bath travel. The collected sample of thread is centrifuged in a spinning bucket rotating at 1400 R. P. M., for onev minute, and the thread is then cut off, and weighed in a closed bottle. The sample is washed free of acid, dried in an oven at 105 C., and weighed again. The ratio between the gel weight of the yarn to the weight of the cellulose in the yarn is referred to as the gel swelling" of the yarn. The gel strength (maximum spinning.

tension) of the yarn is measured with a ten siometer and actually represents the highest ten sion which, can be applied and still have the thread strung up and spinning.

The total length of travel of the yarn in the bath' should be within the range from 80-.-350' inches, depending on the bath composition, spinning speed, and denier of the individual filamerits and the yarn. Theprocess of the present invention is not limited to any particular spinning speed. Also, during the travelof the yarn in the spinning bath, gradual spinning tensions of from 80% oi. the breaking tension of the yarn are imposed thereon.

.In the co-pending applications of William D. Nicoll, Serial'No. 318,326, filed February 10, 1940, and Serial No. 318,327, filed February 10, 1940, are disclosed processes for the tension spinning of filaments for the purpose of imparting crimp thereto, when subsequently relaxed in a relaxing bath. Theuse of manganous sulfate together with zinc sulfatein accordance with the present invention is of great utility in processes relating to the high tension spinning of crimped filaments. Processes of this type are disclosed in Examples VI and VII of the present application.

The invention has been described above with particular reference to the use of single spinning baths. If desired, yarn spun in baths as discussed in detail above may be passed through a secondary water bath or \a secondary .dilute wherein the yarn may be subjected to a further stretching operation such as is well known in the art. This second bath, in which a tension and stretch are imposed on the yarn, is preferably composed of water having a temperature of above C. This stretching'bath may, however, be acid. The acidity of this bath may be equivalent to 3% sulfuric acid, or less. The tension and stretch imposed on the filaments in the secondary stretching bath may be a continuation of the stretch and tension imparted thereto in the spinning bath. v

The present invention is primarily concerned with the composition of the spinning bath employed in the high tension spinning of viscose rayon yarns. The yarns, once spun, can be puritied and dried inr'any known manner with any of the usual purification solutions. The yarn may be spun by the bobbin or bucket process, and the yarn can be purified in, the spun package form, or it can be wound into-skeins and treated in that form. On the other hand, it may be purified in a continuous manner by the use of a conveyor belt or a yarn storing andadvancing reel.

The present invention provides a process for the spinning of viscose rayon yarn having a high tenacity, and a high elongation and greatly increased loop strength.

This invention permits the production of yarn having these improvements in yarn characteristics without, at the same time, adversely affecting the continuity of the spinning operation.

The present invention furthermore, provides an improved process for the tension spinning of crimped yam.

Since it is obvious that many changes and modifications can be made in the details herein disclosed without departing from the nature and spirit of the invention, it is to be understood that the invention is not to be limited to these details except as set forth in the appended claims.

I claim:

1. In the method of producing regenerated cellulose structures by the extrusion of viscose in an aqueous sulfuric acid spinning bath the step which comprises incorporating in said bath from l%-8% maganous sulfate together with 0.1 %-l% zinc sulfate.

in an aqueous sulfuric acid spinning bath'th step which comprises incorporating in said bath from 1%8% manganous sulfate together with 0.1%-1% zinc sulfate.

3. In the method of producing crimped regenerated cellulose filaments by the spinning, under high tension (at least 0.3 gram per denier), of viscose in an aqueous sulfuric acid spinning bath with a subsequent complete relaxation of said filaments in a swelling agent therefor the step which comprises incorporating in said bath from 1%-8% manganous sulfate together 0.1 %-1 zinc sulfate.

4. The method of producing regenerated cellulose structures which comprises the steps of spinning viscose in an aqueous sulfuric acid spinning bath containing from 1%-8% manganous sulfate together with 0.1%-1% zinc sulfate, passing said structures into a second bath, and stretching said structures in said second bath.

5. An aqueous sulfuric acid spinning bath for the spinning, under high tension (0.3 gram per denier), of regenerated cellulose structures from viscose, said bath containing from 1%-8% manganous sulfate together with 0.1%-1% zinc sulfate.

6. An aqueous sulfuric acid spinning bath for the spinning, under high tension (0.3 gram per denier), of regenerated cellulose structures from viscose, said bath containing from 5%-11% sulfuric acid, 18 %-25% sodium sulfate, 0%-4% glucose, 1%-8% manganous sulfate and 0.1%-1% zinc sulfate.

NORMAN LOUIS COX.

with 

